Brake pad and caliper device

ABSTRACT

A brake pad  10  can brake a rotation of a disc  200 . The brake pad  10  includes a friction material  12  provided on the side of the disc  200  and a back plate  11  bonded to the friction material  12  on the opposite side of the disc  200 . A thickness of a central region of the back plate  11  in a rotational direction of the disc  200  is larger than thicknesses of both end regions of the back plate  11  in the rotational direction of the disc. In the case where a minimum value of the thicknesses of the end regions of the back plate  11  is defined as “h 1  [mm]” and a maximum value of the thickness of the central region of the back plate  11  is defined as “h 2  [mm]”, h 1  and h 2  preferably satisfy a relationship of “h 2 −h 1 &lt;3”.

TECHNICAL FIELD

The present invention relates to a brake pad and a caliper device.

BACKGROUND ART

A disc brake has a disc and brake pads, and generally each brake padincludes a lining (friction material) for braking the disc and a backplate for supporting the lining. Since this back plate supports thelining, it is required to have heat resistance, brake resistance, andhigh mechanical strength in a high temperature atmosphere. For thisreason, conventionally, plates made of ceramic or plates made of metalhave been used for the back plate. However, when the plates made ofceramic and the plates made of metal are used for the back plate, thereare problems such as a heavy weight, a long time required for machining,high costs, and the like.

Therefore, recently, it is attempted to use a plate made of a syntheticresin mixed with fibers for the back plate instead of the plates made ofmetal for the purpose of reducing both weight and cost.

As technology relating to this type of back plate, Patent Document 1discloses a back plate that uses a carbon fiber reinforced plasticplate.

However, since a conventional brake pad has low bonding strength betweenthe lining and the back plate, it is difficult to obtain enoughdurability of the brake pad. In particular, there is a problem in thatthe conventional brake pad does not exhibit enough bending rigidity.

PRIOR ART DOCUMENT Patent Document

The Patent Document 1 is JP-A 2010-48387

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

An object of the present invention is to provide a brake pad having highbonding strength between a friction material and a back plate and havingexcellent durability and bending rigidity, and a caliper device providedwith the brake pad.

Means of Solving the Problem

In order to achieve such an object, the present invention includes thefollowing features (1) to (9).

(1) A brake pad for braking a rotation of a disc, the brake padcomprising:

a friction material provided on the side of the disc; and

a back plate bonded to the friction material on the opposite side of thedisc,

wherein a thickness of a central region of the back plate in arotational direction of the disc is larger than thicknesses of both endregions of the back plate in the rotational direction of the disc.

(2) The brake pad according to the above feature (1), wherein in thecase where a minimum value of the thicknesses of the end regions of theback plate is defined as “h₁ [mm]” and a maximum value of the thicknessof the central region of the back plate is defined as “h₂ [mm]”, h₁ andh₂ satisfy a relationship of “h₂−h₁<3”.

(3) The brake pad according to the above feature (1) or (2), wherein aminimum value of the thicknesses of the end regions of the back plate isin the range of 3 to 5 mm.

(4) The brake pad according to any one of the above features (1) to (3),wherein a maximum value of the thickness of the central region of theback plate is in the range of 4 to 7 mm.

(5) The brake pad according to any one of the above features (1) to (4),wherein the thickness of the back plate continuously increases towardthe central region from each of the end regions.

(6) The brake pad according to any one of the above features (1) to (5),wherein the back plate is formed of a back-plate composition including aresin and a plurality of fibers.

(7) The brake pad according to the above feature (6), wherein the fibersare glass fibers.

(8) The brake pad according to the above feature (6) or (7), wherein theresin contains at least one type selected from the group consisting ofphenol resin, epoxy resin, bismaleimide resin, benzoxazine resin, andunsaturated polyester resin.

(9) A caliper device comprising:

the brake pad defined by any one of the above features (1) to (8);

a piston that presses the brake pad toward a disc; and

a caliper in which the piston is put so as to be movable.

Effect of the Invention

According to the present invention, it is possible to provide the brakepad having the high bonding strength between the friction material andthe back plate and having the excellent durability, and the caliperdevice provided with the brake pad.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing one example of a caliperdevice.

FIG. 2 is a cross-sectional view showing one example of the caliperdevice.

FIG. 3 is a planar view showing the first embodiment of the brake pad ofthe present invention.

FIG. 4 is a cross-sectional view showing a first embodiment of a brakepad of the present invention.

FIG. 5 is an illustration showing the brake pad of the present inventionin a state of being arranged corresponding to a disc.

FIG. 6 is a cross-sectional view showing a second embodiment of thebrake pad of the present invention.

MODE FOR CARRYING OUT THE INVENTION

Description will be made on a brake pad and a caliper device of thepresent invention in detail based on preferred embodiments shown in theattached drawings.

First, the caliper device of the present invention will be described indetail.

[Caliper Device]

Each of FIG. 1 and FIG. 2 is a cross-sectional view showing one exampleof the caliper device of the present invention. Each of FIG. 1 and FIG.2 is a view showing the caliper device in a state of being arrangedcorresponding to a disc. In this regard, FIG. 1 is a view showing astate that the disc is not braked (released), and FIG. 2 is a viewshowing a state that the disc is braked by the caliper device. In thisregard, in the following description, the upper side of FIG. 1 isreferred to as the “top”, and the lower side thereof is referred to asthe “bottom”.

A caliper device 100 shown in FIGS. 1 and 2 is used for braking arotating (revolving) disc 200. As shown in FIGS. 1 and 2, the disc 200rotates about a rotation axis 210 in a direction indicated by an arrowA.

The caliper device 100 is provided adjacent to the disc 200. Thiscaliper device 100 includes a caliper 50, a piston 30, and a brake pad10.

The caliper 50 serves as a casing in which the piston 30 is put. Asshown in FIGS. 1 and 2, the caliper 50 has a space 40 opening on thebottom side, and a flow channel 51 communicating with the space 40. Thespace 40 is of a cylindrical shape, and the piston 30 is put (housed) inthe space 40.

A ring-shaped groove 55 is formed on an inner circumferential surface ofthe caliper 50 defining the space 40. Inside the groove 55, provided(inserted) is a ring-shaped seal member 60 formed of an elasticmaterial. Moreover, the seal member 60 makes pressure contact with anouter circumferential surface of the piston 30 such that the piston 30can slide.

In this regard, the single seal member 60 is provided in the space 40 inthis embodiment, but the number of the seal members is not limitedthereto. For example, two or more seal members may be parallel providedalong a vertical direction of FIG. 1 in the space 40. Further, in thisregard, the number of the seal members may be appropriately setdepending on the intended purpose of the caliper device 100, requiredperformance thereof, and the like.

The seal structure formed by such a seal member is also obviously notlimited to the illustrated structure.

The piston 30 has a function of pressing the brake pad 10 toward thedisc 200.

As described above, the piston 30 is put in the space 40, and the sealmember 60 makes pressure contact with the outer circumferential surfaceof the piston 30. Therefore, the space 40 is liquid-tightly sealed bythe seal member 60.

The space 40 is filled with a brake fluid. In the caliper device 100,the brake fluid can be supplied into the space 40 and discharged out ofthe space 40 via the flow channel 51 by using a hydraulic device notillustrated. By providing the seal member 60, it is possible to preventleakage of the brake fluid out of the space 40 and penetration offoreign substance into the space 40.

The brake pad 10 has a function of controlling the rotation of the disc200 (decreasing a rotational speed thereof) due to a frictional forcegenerated between the brake pad 10 and the disc 200 by being madepressure contact with the disc 200 during braking.

The brake pad 10 is provided between the piston 30 and the disc 200. Thebrake pad 10 is composed of a bonded body in which a back plate 11 and afriction material 12 are bonded together. The back plate 11 ispositioned on the side of the piston 30, and the friction material 12 ispositioned on the side of the disc 200. A top surface of the back plate11 makes contact with a bottom surface of the piston 30. In this regard,the top surface of the back plate 11 and the bottom surface of thepiston 30 may be bonded or not bonded together. Moreover, a bottomsurface of the friction material 12 faces a top surface of the disc 200.

The caliper device of the present invention can be used for either anopposing type caliper device or a floating type caliper device.

In the case of the opposing type caliper device, while not illustrated,a control mechanism having the same configuration as a control mechanismincluding the above mentioned space 40, piston 30 and brake pad 10 isprovided on the bottom side of the disc via a center line 220 of thedisc 200 (with a mirror image arrangement). In other words, in the caseof the opposing type caliper device, a pair of control mechanisms eachincluding the space, the piston and the brake pad is provided via thedisc 200. According to the opposing type caliper device having such aconfiguration, both the brake pads provided in a pair move with respectto the caliper 50 and sandwich the disc 200, to thereby brake therotation of the disc 200. Moreover, the number of sets (the number ofpairs) of such control mechanisms is not limited to one set, and may be,for example, a plurality of sets such as two sets or three sets.

On the other hand, in the case of the floating type caliper device,while not illustrated, a brake pad having the same configuration as theabove mentioned brake pad 10 is provided on the bottom side of the disc200 via the center line 220 of the disc 200, and fixed to the caliper 50at this position. In other words, a pair of brake pads including thebrake pad 10 movable with respect to the caliper 50 and the brake padfixed to the caliper 50 is provided via the disc. Moreover, the numberof sets (the number of pairs) of the brake pads is not limited to oneset, and may be, for example, a plurality of sets such as two or threesets.

Next, operation of the caliper device 100 will be described.

In the caliper device 100, during non-braking (in an initial state), thebottom surface of the friction material 12 is separated at a slightdistance from the top surface of the disc 200.

From this state, when braking the rotating disc 200, the brake fluid issupplied into the space 40 via the flow channel 51 by using the abovementioned hydraulic device. At this time, a pressure (a fluid pressure)of the brake fluid with respect to the piston 30 in the space 40increases, so that the piston 30 moves toward the disc 200. At the sametime, the brake pad 10 also moves downward in FIG. 1 along with themoving piston 30, and as shown in FIG. 2, the friction material 12thereof makes pressure contact with the disc 200. As a result, thefrictional force is generated between the friction material 12 of thebrake pad 10 and the disc 200, and thus the rotation of the disc 200 issuppressed.

In this regard, when the piston 30 has moved to the side of the disc dueto the increase of the fluid pressure of the brake fluid in the space40, a portion of the seal member 60 that makes pressure contact with thepiston 30 is pulled to the side of the disc 200, so that the seal member60 undergoes elastic deformation.

On the other hand, when releasing the braking of the disc 200, thesupply of the brake fluid into the space 40 by using the hydraulicdevice is stopped, or the brake fluid is transferred from the space 40via the flow channel 51 to the hydraulic device. By doing so, a part ofthe brake fluid in the space 40 is discharged out of the space 40 viathe flow channel 51, to thereby decrease the pressure (the fluidpressure) of the brake fluid with respect to the piston 30. For thisreason, a force pressing the piston 30 toward the disc 200 decreases, sothat the seal member 60 becomes deformed to the non-braking state due toa restoring force thereof. This allows the piston 30 to move in adirection of separating from the disc 200 (upward). At this time, thebottom surface of the friction material 12 separates from the topsurface of the disc 200, or a pressure contact force of the bottomsurface of the friction material 12 to the top surface of the disc 200decreases. As a result, the braking of the disc 200 is released.

In the case where the caliper device of the present invention is theopposing type, the respective pistons and brake pads, which are providedopposite to each other via the center line 220 of the disc 200, operatein the same manner as described above both during braking and duringreleasing the braking. In the case of the opposing type caliper device,it is possible to obtain a larger braking force by sandwiching the disc200 from both sides by at least one pair of brake pads during braking.

Further, in the case of the floating type, the disc 200 is braked bybeing sandwiched by the brake pad 10 movable with respect to the caliper50 and the brake pad fixed to the caliper 50. In other words, when thebrake pad 10 moves and presses the disc 200, the caliper 50 moves in adirection separating from the disc 200 (upward) due to a reaction forcethereof. By the upward moving of the caliper 50, the brake pad (notillustrated) also provided opposite to the brake pad 10 and fixed to thecaliper 50 moves upward, namely, in a direction approaching the disc200, and presses the disc 200. As a result, the disc 200 is sandwichedand braked by the movable brake pad 10 and the fixed brake pad.

The intended purpose of the caliper device of the present invention isnot particularly limited, and the device can be used in, for example,airplanes, vehicles (automobiles), motorcycles, bicycles, rail cars,elevators, robots, construction machineries, agricultural machineries,other industrial machineries, and the like.

First Embodiment of Brake Pad

Next, a first embodiment of the brake pad provided in the caliper deviceof the present invention will be described.

FIG. 3 is a planar view showing the first embodiment of the brake pad ofthe present invention. FIG. 4 is a cross-sectional view showing thefirst embodiment of the brake pad of the present invention. FIG. 5 is anillustration showing the brake pad of the present invention in a stateof being arranged corresponding to the disc. In this regard, a“rotational direction of the disc 200” described below means arotational direction of the disc 200 at a position where the brake pad10 is attached to the piston 30 of the caliper device 100, and is adirection indicated by an arrow A in FIGS. 4 and 5.

The brake pad of the present invention can control the rotation of thedisc due to the frictional force generated between the brake pad and thedisc by being made contact with the disc during braking.

As described above, the brake pad 10 is composed of the bonded body inwhich the back plate 11 and the friction material 12 are bondedtogether. In this embodiment, as shown in FIG. 4, thicknesses of bothends (both end regions) of the back plate 11 in the rotational directionof the disc 200 are substantially equal to each other, and thethicknesses of the both ends are smaller than a thickness of asubstantial center (a central region) of the back plate 11 in therotational direction of the disc 200. Namely, the thickness of thesubstantial center of the back plate 11 in the rotational direction ofthe disc 200 (in FIG. 4, a thickness indicated by “h₂”) is larger thanthe thicknesses of the both ends of the back plate 11 in the rotationaldirection of the disc 200 (in FIG. 4, a thickness indicated by “h₁”).

In other words, as shown in FIG. 4, a surface (a surface making contactwith the piston 30) of the back plate 11 opposite to a surface (abonding surface) thereof, to which the friction material 12 is bonded,is formed into a substantially flat surface, and the bonding surfacethereof is formed into a convex curved surface protruding toward theside of the friction material 12 (the disc 200). Namely, the substantialcenter of the back plate 11 in the rotational direction of the disc 200protrudes toward the side of the friction material 12. On the otherhand, a substantial center of a surface (a bonding surface) of thefriction material 12, to which the back plate 11 is bonded, in therotational direction of the disc 200 is recessed toward the side of thedisc 200 so as to correspond to the shape of the bonding surface of theback plate 11.

The back plate 11 and the friction material 12 are bonded together in astate that the bonding surface (the convex curved surface) of the backplate 11 and the bonding surface of the friction material 12 make closecontact with each other. In such a bonded body, a contact area betweenthe back plate 11 and the friction material 12 can be increased incomparison with a case where both the bonding surface of the back plateand the bonding surface of the friction material are formed into flatsurfaces. Therefore, it is possible to improve bonding strength betweenthe back plate 11 and the friction material 12. Further, it is alsopossible to improve durability of the back plate 11 against a forceapplied thereto in the rotational direction of the disc 200.Furthermore, by increasing the thickness of the central region of theback plate 11, it is possible to enhance bending rigidity of the backplate 11. This makes it possible to improve bending rigidity of thewhole brake pad 10.

In this embodiment, as shown in FIG. 4, the thickness of the back plate11 continuously increases toward the central region thereof in therotational direction of the disc 200 from each of the ends (each of theend regions) thereof in the rotational direction of the disc 200. Bythis configuration, it is possible to more enhance the bending rigidityof the back plate 11, while improving the durability of the back plate11 against the force applied thereto in the rotational direction of thedisc 200.

Further, in the case where a minimum value of the thicknesses of the endregions of the back plate 11 is defined as “h₁ [mm]” and a maximum valueof the thickness of the central region of the back plate 11 is definedas “h₂ [mm]”, h₁ and h₂ preferably satisfy a relationship of “h₂−h₁<3”,and more preferably satisfy a relationship of “1<h₂−h₁<3”. By satisfyingsuch a relationship, it is possible to further improve the bondingstrength between the back plate 11 and the friction material 12.Further, it is also possible to more effectively improve the durabilityof the back plate 11 against the force applied thereto in the rotationaldirection of the disc 200. In contrast, if the value “h₂−h₁” exceeds theabove upper limit value, there is a fear that the thickness of thecentral region of the friction material 12 in the rotational directionof the disc 200 cannot be sufficiently increased depending on a size andthe like of the brake pad 10.

The minimum value of the thicknesses of the end regions of the backplate 11 is preferably in the range of 3 to 5 mm, and more preferably inthe range of 4 to 5 mm. This makes it possible to reduce a weight of thebrake pad 10 and to more effectively improve the durability of the backplate 11 against the force applied thereto in the rotational directionof the disc 200.

The maximum value of the thickness of the central region of the backplate 11 is preferably in the range of 4 to 7 mm, and more preferably inthe range of 5 to 6 mm. This makes it possible to reduce a weight of thebrake pad 10, and to further enhance the bending rigidity of the backplate 11.

Moreover, in this embodiment, as shown in FIG. 3, a planar shape of thebrake pad 10 (the friction material 12 and the back plate 11) is asubstantially quadrilateral shape. Furthermore, the friction material 12has a planar size smaller than a planar size of the back plate 11, andis positioned so as to be included within the back plate 11 in theplanar view.

In this regard, each of the planar shapes of the friction material 12and the back plate 11 is the substantially quadrilateral shape in thisembodiment, but is not limited thereto. Each of the planar shapes of thefriction material 12 and the back plate 11 may be, for example, asubstantially circular shape, a polygonal shape, or the like.Furthermore, these planar shapes may also be, respectively, differentshapes. In this regard, these planar shapes may be appropriately setdepending on the intended purpose of the brake pad 10.

Further, the thickness of the back plate 11 continuously increasestoward the substantial center (the central region) thereof in therotational direction of the disc 200 from each of the ends (each of theend regions) thereof in the rotational direction of the disc 200 in theabove description, but may intermittently increase toward thesubstantial center from each of the ends.

Hereinafter, constituent materials of the friction material 12 and theback plate 11 included in the brake pad 10 will be described in detail.

<Friction Material 12>

The friction material 12 has a function of suppressing the rotation ofthe disc 200 due to friction generated by being made contact with thedisc 200 during braking.

When the friction material 12 makes contact with the disc 200 duringbraking, it generates frictional heat due to the friction between thefriction material 12 and the disc 200. Therefore, it is preferred thatthe constituent material of the friction material 12 has excellent heatresistance in order to resist the frictional heat during braking.Concrete examples of the constituent material thereof include, but arenot particularly limited to, mixtures containing fiber materials such asrock wool, Kevlar fiber and copper fiber; bonding materials such as aresin; and fillers such as barium sulfate, zirconium silicate, cashewdust and graphite.

Moreover, an average thickness of the friction material 12 is notparticularly limited, but is preferably in the range of 3 to 15 mm, andmore preferably in the range of 5 to 12 mm. If the average thickness ofthe friction material 12 is less than the above lower limit value, thereis a case that mechanical strength of the friction material 12 isreduced depending on the constituent material thereof and the like, sothat it easily breaks and thus becomes a short life-span. On the otherhand, if the average thickness of the friction material 12 exceeds theabove upper limit value, there is a case that the entire caliper device100 including the friction material 12 becomes a slightly large size.

The back plate 11 is hard and has high mechanical strength. For thisreason, the back plate 11 is difficult to be deformed, and thus canreliably support the friction material 12 and uniformly transmit apressing force of the piston to the friction material 12 during braking.Moreover, the back plate 11 can also make it difficult to transmit thefrictional heat and vibration, which are generated by sliding contact ofthe friction material 12 to the disc 200, to the piston during braking.

The back plate 11 is preferably formed of a back-plate composition (acomposition for forming the back plate of the brake pad) including aresin and a plurality of fibers. Especially, the back plate 11 morepreferably is formed of the back-plate composition including the resin,a plurality of first fibers and a plurality of second fibers.

Hereinafter, the back-plate composition constituting the back plate 11will be described in detail.

<<Back-Plate Composition>>

Hereinafter, each material constituting the back-plate composition willbe described in detail.

(i) Resin

In this embodiment, the back-plate composition contains the resin.

In this regard, in this embodiment, the resin may be in any state suchas a solid state, a liquid state, or a semisolid state at roomtemperature.

Examples of the resin include curable resins such as a thermosettingresin, a photocurable resin, a reactive curable resin and ananaerobically curing resin. Among them, particularly, the thermosettingresin is preferable because it has excellent mechanical properties suchas linear expansion coefficient and elastic modulus after curing.

Examples of the thermosetting resin include phenol resin, epoxy resin,bismaleimide resin, urea resin, melamine resin, polyurethane resin,cyanate ester resin, silicone resin, oxetane resin, (meth)acrylateresin, unsaturated polyester resin, diallyl phthalate resin, polyimideresin, benzoxazine resin, and the like. One type of them can be usedalone, or two or more types of them can be used in combination. Amongthem, particularly, the phenol resin, the epoxy resin, the bismaleimideresin, the benzoxazine resin, and the unsaturated polyester resin arepreferable, and the phenol resin is more preferable as the thermosettingresin. This makes it possible for the back plate 11 to have particularlyexcellent heat resistance to the frictional heat generated when thefriction material 12 makes contact with the disc 200 during braking.

Examples of the phenol resin include novolac type phenol resins such asphenol novolac resin, cresol novolac resin, bisphenol A novolac resinand aryl alkylene type novolac resin; resol type phenol reins such asunmodified resol phenol resin and resol phenol resin modified by an oilsuch as tung oil, linseed oil or walnut oil. One type of them can beused alone, or two or more types of them can be used in combination.Among them, particularly, the phenol novolac resin is preferable as thephenol resin. This makes it possible to manufacture the back plate 11 ata low cost and with high dimensional accuracy, and to obtain the backplate 11 having particularly superior heat resistance.

A weight average molecular weight of the phenol resin is notparticularly limited, but is preferably in the range of about 1,000 to15,000. If the weight average molecular weight is less than the abovelower limit value, there is a case that it becomes difficult to preparethe back-plate composition due to too low viscosity of the resin. On theother hand, if the weight average molecular weight exceeds the aboveupper limit value, there is a case that moldability of the back-platecomposition decreases because a melt viscosity of the resin becomeshigh. For example, the weight average molecular weight of the phenolresin can be measured by gel permeation chromatography (GPC), and can bestipulated as a polystyrene-converted weight molecular weight.

Examples of the epoxy resin include bisphenol type epoxy resins such asbisphenol A type epoxy resin, bisphenol F type epoxy resin and bisphenolAD type epoxy resin; novolac type epoxy resins such as phenol novolactype epoxy resin and cresol novolac type epoxy resin; brominated typeepoxy resins such as brominated bisphenol A type epoxy resin andbrominated phenol novolac type epoxy resin; biphenyl type epoxy resin;naphthalene type epoxy resin; tris(hydroxyphenyl) methane type epoxyresin; and the like. One type of them can be used alone, or two or moretypes of them can be used in combination. Among them, particularly, thebisphenol A type epoxy resin, phenol novolac type epoxy resin and cresolnovolac type epoxy resin each having a relatively low molecular weightare preferable as the epoxy resin. This makes it possible to increaseflowability of the back-plate composition. As a result, it is possibleto further improve handling property and the moldability of theback-plate composition when manufacturing the back plate 11. Moreover,from the viewpoint of further improving the heat resistance of the backplate 11, the phenol novolac type epoxy resin and the cresol novolactype epoxy resin are preferable, and the tris(hydroxyphenyl) methanetype epoxy resin is particularly preferable as the epoxy resin.

The bismaleimide resin is not particularly limited as long as it is aresin having maleimide groups at both ends of a molecular chain thereof,but is preferably a resin having a phenyl group in addition to themaleimide groups. Specifically, as the bismaleimide resin, for example,a resin represented by the following chemical formula (1) can be used.In this regard, the bismaleimide resin may also have a maleimide groupbonded at a position other than both ends of the molecular chainthereof.

In the chemical formula (1), each of R¹ to R⁴ is a hydrogen atom or asubstituted or unsubstituted hydrocarbon group having a carbon number of1 to 4, and R⁵ is a substituted or unsubstituted organic group. Here,the organic group means a hydrocarbon group that may contain aheteroatom such as 0, S or N. R⁵ is preferably a hydrocarbon grouphaving a main chain in which a methylene group(s), an aromatic ring(s)and an ether bond(s) (—O—) are bonded in any order, and is morepreferably a hydrocarbon group in which a total number of the methylenegroup(s), the aromatic ring(s) and the ether bond(s) contained in themain chain thereof is 15 or less. In this regard, the main chain mayhave a substituent group and/or a side chain bonded in a middle thereof.Concrete examples thereof include a hydrocarbon group having a carbonnumber of 3 or less, a maleimide group, a phenyl group, and the like.

Specifically, examples of the bismaleimide resin includeN,N′-(4,4′-diphenyl methane)bismaleimide,bis(3-ethyl-5-methyl-4-maleimidephenyl) methane,2,2-bis[4-(4-maleimidephenoxy)phenyl]propane, m-phenylene bismaleimide,p-phenylene bismaleimide, 4-methyl-1,3-phenylene bismaleimide,N,N′-ethylene dimaleimide, N,N′-hexamethylene dimaleimide, and the like.One type of them can be used alone, or two or more types of them can beused in combination.

An amount of the resin contained in the back-plate composition is notparticularly limited, but is preferably in the range of 20 to 80 mass %,and is more preferably in the range of 30 to 50 mass %.

If the amount of the resin is less than the above lower limit value,there is a case that the resin cannot have sufficient binding strengthwith the other materials constituting the back-plate composition(particularly, the first fibers and the second fibers) depending on thetypes thereof. On the other hand, if the amount of the resin exceeds theabove upper limit value, there is a case that amounts of the firstfibers and the second fibers described below relatively decreases, andthus effects to be obtained by including the first fibers and the secondfibers are not adequately exhibited.

(ii) Fibers

In this embodiment, the back-plate composition includes the plurality offibers. The plurality of fibers preferably includes the plurality offirst fibers, and more preferably includes the plurality of first fibersand the plurality of second fibers.

Namely, the back-plate composition preferably includes a fiber groupthat is a mass of the plurality of fibers, more preferably includes atleast a first fiber group that is a mass of the plurality of firstfibers, and even more preferably includes the first fiber group and asecond fiber group that is a mass the plurality of second fibers.

The first fibers belonging to the first fiber group have an averagelength longer than an average length of the second fibers belonging tothe second fiber group (in other words, the second fibers belonging tothe second fiber group have the average length shorter than the averagelength of the first fibers belonging to the first fiber group). In thisway, in the case where the back-plate composition includes two types offibers having different average lengths, it is possible to improve themoldability (ease of molding) thereof, and to increase the mechanicalstrength of the molded back plate 11.

Hereinafter, such first fibers and second fibers will be described indetail.

In the case where the average length of the first fibers is “L1” [μm],and the average length of the second fibers is “L2” [μm], “L2”/“L1” ispreferably in the range of 0.001 to 0.5, more preferably in the range of0.01 to 0.4, and even more preferably in the range of 0.015 to 0.3. Ifthe ratio “L2”/“L1” of the average length “L2” of the second fibers tothe average length “L1” of the first fibers is within the above range,it is possible to further improve the moldability of the back-platecomposition, and to particularly increase the dimensional accuracy andthe mechanical strength of the back plate 11.

When the two types of fibers having different average lengths arecompared, the first fibers having lengths longer than lengths of thesecond fibers contribute primarily to securing the mechanical strengthof the back plate 11 and to shape stability of the back plate 11.

On the other hand, the second fibers having the shorter lengths alsocontribute to the shape stability of the back plate 11, but also assumea role of mainly filling (squeezing) gaps between the first fibershaving relatively long lengths. In other words, the second fiberssqueeze the gaps between the first fibers, thereby increasing themechanical strength of the back plate 11 in portions where the firstfibers are not present, namely, the second fibers exhibit an action ofaiding the effects of the first fibers (reinforcing action). Morespecifically, because of the lengths of the first fibers, the firstfibers have a high tendency to orient along a surface direction of theback plate 11. In contrast, the second fibers squeeze the gaps betweenthe first fibers, but also exhibit a tendency to orient along thesurface direction of the back plate 11 and to orient along a directionthat differs from the surface direction of the back plate 11. In thisway, different orientation states of the first fibers and the secondfibers makes it possible to sufficiently impart the mechanical strengthand the shape stability to the back plate 11 even if both the firstfibers and the second fibers are used in small amounts.

The above function is remarkably exhibited particularly by setting theratio “L2”/“L1” within the above range. Furthermore, in the case wherethe first fibers and the second fibers are formed of the same materialor the same type of material, this tendency is remarkably obtained.

The average length “L1” of the first fibers is preferably in the rangeof 5 to 50 mm, and more preferably in the range of 8 to 12 mm. If theaverage length “L1” of the first fibers is less than the above lowerlimit value, there is a case that the shape stability of the back plateis not sufficiently obtained depending on the constituent material ofthe first fibers and an amount thereof. On the other hand, if theaverage length “L1” of the first fibers exceeds the above upper limitvalue, there is a case that the flowability of the back-platecomposition is not sufficiently obtained when molding the back plate 11.

Moreover, the average length “L2” of the second fibers is preferably inthe range of 50 μm to 10 mm, more preferably in the range of 150 μm to 5mm, and even more preferably in the range of 200 μm to 3 mm. If theaverage length “L2” of the second fibers is less than the above lowerlimit value, for example, when the amount of the first fibers is small,there is a case that it is necessary to set the amount of the secondfibers contained in the back-plate composition to a relatively largevalue in order to increase the reinforcing action which aids the effectobtained by the first fibers. On the other hand, if the average length“L2” of the second fibers exceeds the above upper limit value, when theamount of the first fibers is large, there is a case that the amount ofthe second fibers that squeeze the gaps between the first fibersdecreases.

An average diameter “D1” of the first fibers is preferably in the rangeof 5 to 20 μm, more preferably in the range of 6 to 18 μm, and even morepreferably in the range of 7 to 16 μm. If the average diameter “D1” ofthe first fibers is less than the above lower limit value, there is acase that the first fibers easily break when molding the back plate 11depending on the constituent material of the first fibers and the amountthereof. On the other hand, if the average diameter “D1” of the firstfibers exceeds the above upper limit value, there is a case that theback plate 11 has variation in strength between areas where the firstfibers are present in a relatively large amount and areas where they arepresent in a relatively small amount.

Further, an average diameter “D2” of the second fibers is preferably inthe range of 5 to 20 μm, more preferably in the range of 6 to 18 μm, andeven more preferably in the range of 7 to 16 μm. If the average diameter“D2” of the second fibers is less than the above lower limit value,there is a case that the second fibers easily break when molding theback plate 11 depending on the constituent materials of the first fibersand the second fibers and the amounts thereof. On the other hand, if theaverage diameter “D2” of the second fibers exceeds the above upper limitvalue, there is a case that the second fibers become difficult tosqueeze the gaps between the first fibers depending on the amount of thefirst fibers.

A cross-sectional shape of each first fiber is not particularly limited,and may be any shape including a substantially circular shape such as acircular shape or an elliptical shape; a polygonal shape such as atriangular shape, a quadrilateral shape or a hexagonal shape; a flatshape; an irregular shape such as a star shape; and the like. Amongthem, particularly, the cross-sectional shape of each first fiber ispreferably the substantially circular shape or the flat shape. Thismakes it possible to improve smoothness of the surface of the back plate11.

A cross-sectional shape of each second fiber is not particularlylimited, and may be any shape including a substantially circular shapesuch as a circular shape or an elliptical shape; a polygonal shape suchas a triangular shape or a quadrilateral shape; a flat shape; and anirregular shape such as a star shape. Among them, particularly, thecross-sectional shape of each second fiber is preferably thesubstantially circular shape or the flat shape. This makes it possibleto further improve the handling property of the back-plate compositionwhen molding it, to thereby highly increase the moldability thereof.

In the back-plate composition, the first fibers may be present as singlebodies, or may be present as fiber bundles in which several first fibersare compactly integrated together. If the first fibers form the fiberbundles, the fiber bundles thereof may be of any shape such as a twistedfiber shape, a linear shape or a netlike shape. The same also applies tothe second fibers.

Examples of the first fibers and the second fibers, respectively,include organic fibers such as aramid fibers, acrylic fibers, nylonfibers (aliphatic polyamide fibers) and phenol fibers; inorganic fiberssuch as glass fibers, carbon fibers, ceramic fibers, rock wool,potassium titanate fibers and basalt fibers; metal fibers such asstainless steel fibers, steel fibers, aluminum fibers, copper fibers,brass fibers and bronze fibers; and the like. One type of them can beused alone, or two or more types of them can be used in combination.Among them, particularly, the first fibers and the second fibers are,respectively, preferably the aramid fibers, the carbon fibers, or theglass fibers, and at least one type of the first fibers and the secondfibers (the first fibers and/or the second fibers) are more preferablythe glass fibers.

If the glass fibers are used, it is possible to improve homogeneity ofthe back-plate composition per unit volume, to thereby make themoldability of the back-plate composition particularly good.Furthermore, by improving the homogeneity of the back-plate composition,it is possible to improve uniformity of internal stress in the formedback plate 11, to thereby reduce waviness of the back plate 11.Moreover, it is also possible to further improve wear resistance of theback plate 11 under high load. Further, if the carbon fibers or thearamid fibers are used, it is possible to further improve the mechanicalstrength of the back plate 11, and to more reduce the weight of the backplate 11.

Concrete examples of glass constituting the glass fibers includeE-glass, C-glass, A-glass, S-glass, D-glass, NE-glass, T-glass, andH-glass. Among them, particularly, the E-glass, the T-glass, or theS-glass is preferable as the glass constituting the glass fibers. Byusing such glass fibers, it is possible to impart higher elasticity tothe first fibers and/or the second fibers, and to reduce thermalexpansion coefficient thereof.

Moreover, concrete examples of the carbon fibers include high-strengthcarbon fibers each having a tensile strength of 3,500 MPa or more, andhigh-elastic modulus carbon fibers each having an elastic modulus of 230GPa or more. The carbon fibers may be either polyacrylonitrile (PAN)based carbon fibers or pitch-based carbon fibers, but are preferably thepolyacrylonitrile based carbon fibers because of their high tensilestrength.

Furthermore, aramid resin constituting the aramid fibers may have eithera meta type chemical structure or a para type chemical structure.

The first fibers and the second fibers may be, respectively, formed ofdifferent materials, but are preferably formed of the same material orthe same type of material. By using the same material or the same typeof material as the constituent materials of the first fibers and thesecond fibers, mechanical strengths of the first fibers and the secondfibers become close to each other, and thus the handling propertythereof when preparing the back-plate composition is further improved.

Here, the phrase “the same type” used in this specification means thatif the first fibers are the glass fibers, the second fibers are also theglass fibers. In this regard, differences of glass varieties such as theE-glass, the C-glass are included in the range of “the same type”.

Moreover, in this specification, the phrase “the same” means that ifboth the first fibers and the second fibers are the glass fibers and thefirst fibers are fibers formed of the E-glass, the second fibers arealso fibers formed of the E-glass.

If the first fibers and the second fibers are formed of the same type ofmaterial, particularly, the first fibers and the second fibers arepreferably the aramid fibers, the carbon fibers, or the glass fibers,and more preferably the glass fibers. In the case where both the firstfibers and the second fibers are the glass fibers, the mechanicalstrengths thereof become close to each other, and the handling propertythereof when preparing the back-plate composition becomes better.Furthermore, since both the first fibers and the second fibers can havethe above mentioned merits of the glass fibers, the flowability of theback-plate composition is further improved, and the moldability of theback-plate composition is particularly good.

Moreover, in the case where both the first fibers and the second fibersare the glass fibers and are formed of the same glass, particularly, thetype of glass is preferably the E-glass. In this case, the abovementioned effects become more remarkable.

It is preferred that at least one type of the first fibers and thesecond fibers (the first fibers and/or the second fibers) are subjectedto a surface treatment in advance.

By subjecting them to the surface treatment in advance, dispersibilityof the first fibers and/or the second fibers in the back-platecomposition can be increased, an adhesive force thereof with respect tothe resin can be increased, and the like.

Examples of a method for such a surface treatment include a couplingagent treatment, an oxidation treatment, an ozone treatment, a plasmatreatment, a corona treatment, and a blast treatment. One type of themcan be used alone, or two or more types of them can be used incombination. Among them, particularly, the method for the surfacetreatment is preferably the coupling agent treatment.

The coupling agent used for the coupling agent treatment is notparticularly limited, and can be appropriately selected depending on thetype of the resin.

Examples of the coupling agent include a silane based coupling agent, atitanium based coupling agent, and an aluminum based coupling agent. Onetype of them can be used alone, or two or more types of them can be usedin combination. Among them, particularly, the coupling agent ispreferably the silane based coupling agent. This makes it possible toespecially improve adhesiveness of the first fibers and/or the secondfibers with respect to the resin.

Examples of the silane based coupling agent include an epoxy silanecoupling agent, a cationic silane coupling agent, an amino silanecoupling agent, a vinyl silane coupling agent, a mercapto silanecoupling agent, a methacrylic silane coupling agent, a chlorosilanecoupling agent, an acrylic silane coupling agent, and the like.

In the back plate 11, for example, the first fibers and the secondfibers may, respectively, orient along a thickness direction of the backplate 11, may orient along a surface direction of the back plate 11, mayorient along a direction inclined at a predetermined angle with respectto the thickness direction or the surface direction of the back plate11, or may not orient (may be non-oriented). However, of the firstfibers and the second fibers, at least the first fibers preferablyorient along the surface direction of the back plate 11. This makes itpossible to further reduce dimensional variation along the surfacedirection of the back plate 11. As a result, it is possible to morereliably suppress or prevent deformation such as warpage of the backplate 11. In this regard, the phrase “the first fibers and the secondfibers orient along the surface direction of the back plate 11” means astate that the first fibers and the second fibers orient substantiallyparallel to the surface of the back plate 11.

Furthermore, in the case where the first fibers and/or the second fibersorient along the surface direction of the back plate 11, in a state thatthe back plate 11 is, as shown in FIG. 5, arranged corresponding to thedisc 200, the first fibers and/or the second fibers may be randomlypresent without orienting along a specific direction within the surfacethereof, may orient along a radial direction of the disc 200, may orientalong an advancing direction A of the disc 200, or may orient along anintermediate direction (a predetermined direction) of these directions.In this regard, in the case where, of the first fibers and the secondfibers, at least the first fibers are randomly present without orientingalong the specific direction within the surface thereof, the back plate11 can have high bending strength and compression strength uniformly inall directions within the surface thereof. Moreover, in the case whereat least the first fibers orient along the advancing direction A of thedisc 200 braked by the brake pad 10, it is possible to selectivelyincrease the bending strength and the compression strength of the backplate 11 along the advancing direction A of the rotating disc 200. As aresult, braking performance of the caliper device 100 provided with theback plate 11 to the disc 200 becomes particularly good. In this regard,the phrase “the first fibers or the second fibers orient along theadvancing direction A of the disc 200” means that the first fibers orthe second fibers orient along the surface direction of the back plate11, and orient along the advancing direction A of the disc 200 in asubstantially parallel manner.

A total amount of the first fibers and the second fibers contained inthe back-plate composition is preferably in the range of 20 to 80 mass%, and more preferably in the range of 30 to 70 mass %. If the totalamount of the first fibers and the second fibers is less than the abovelower limit value, there is a case that the mechanical strength of theback plate 11 decreases depending on the materials of the first fibersand the second fibers. On the other hand, if the total amount of thefirst fibers and the second fibers exceeds the above upper limit value,there is a case that the flowability of the back-plate compositiondecreases when molding the back plate 11.

In the case where the amount of the first fibers contained in theback-plate composition is “X1” [mass %] and the amount of the secondfibers contained therein is “X2” [mass %], “X2”/“X1” is preferably inthe range of 0.05 to 1, and more preferably in the range of 0.1 to 0.25.If the ratio “X2”/“X1” of the amount of the second fibers to the amountof the first fibers is less than the above lower limit value, when thelengths of the first fibers are relatively long, breakage and the likeof the first fibers more easily occurs when manufacturing the back plate11. On the other hand, if the ratio “X2”/“X1” of the amount of thesecond fibers to the amount of the first fibers exceeds the above upperlimit value, when the lengths of the first fibers are relatively short,the mechanical strength of the back plate 11 often decreases. Further,if the first fibers and the second fibers are formed of the samematerial or the same type of material, these tendencies becomesignificant.

The amount of the first fibers is preferably in the range of 35 to 80mass %, more preferably in the range of 40 to 75 mass %, and even morepreferably in the range of 50 to 65 mass %. If the amount of the firstfibers is less than the above lower limit value, there is a case thatshrinkage percentage of the back plate 11 when molding it slightlyincreases depending on the lengths of the first fibers and the amount ofthe second fibers. If the amount of the first fibers exceeds the aboveupper limit value, there is a case that the breakage and the like of thefirst fibers more easily occurs when manufacturing the back plate 11depending on the lengths of the first fibers and the amount of thesecond fibers.

The amount of the second fibers is preferably in the range of 2 to 40mass %, more preferably in the range of 3 to 35 mass %, and even morepreferably in the range of 5 to 30 mass %. If the amount of the secondfibers is less than the above lower limit value, there is a case thatmechanical properties of the back plate 11 are not sufficiently obtaineddepending on the lengths of the second fibers and the amount of thefirst fibers. On the other hand, if the amount of the second fibersexceeds the above upper limit value, there is a case that theflowability of the back-plate composition when molding the back plate 11is not sufficiently obtained.

In this regard, the back-plate composition may also contain one or aplurality of third fibers, and the like in addition to the plurality offirst fibers (the first fiber group) and the plurality of second fibers(the second fiber group) as described above.

As necessary, the back-plate composition may further contain a curingagent, a curing aid agent, a filler, a mold release agent, a pigment, asensitizer, an acid proliferating agent, a plasticizer, a flameretardant, a stabilizing agent, an antioxidant, an antistatic agent, andthe like.

The curing agent can be appropriately selected and used depending on thetype and the like of the resin, and is not limited to a specificcompound.

For example, if the phenol resin is used as the resin, the curing agentcan be selected from epoxy type compounds each having two or morefunctional groups, isocyanates, hexamethylene tetramine, and the like,and used.

Furthermore, if the epoxy resin is used as the resin, the curing agentcan be selected from amine compounds such as aliphatic polyamine, anaromatic polyamine and dicyamine diamide; acid anhydrides such asalicyclic acid anhydrides and aromatic acid anhydrides; polyphenolcompounds such as novolac type phenol resins; imidazole compounds; andthe like, and used. Among them, the novolac type phenol resin ispreferably selected as the curing agent from a viewpoint of handlingproperty and also from an environmental perspective.

In particular, when the phenol novolac type epoxy resin, the cresolnovolac type epoxy resin, or the tris(hydroxyphenyl) methane type epoxyresin is used as the epoxy resin, the novolac type phenol resin ispreferably selected and used as the curing agent. This makes it possibleto improve the heat resistance of a cured product of the back-platecomposition (the back plate 11).

In the case where the curing agent is used, an amount of the curingagent contained in the back-plate composition is appropriately setdepending on the types and the like of the curing agent and the resin tobe used, but is, for example, preferably in the range of 0.1 to 30 mass%. This makes it possible to easily form the back plate 11 into anyshapes.

Moreover, as the curing aid agent, an imidazole compound, a tertiaryamine compound, an organic phosphorous compound, and the like can beused, but it is not particularly limited thereto.

In the case where the curing aid agent is used, an amount of the curingaid agent contained in the back-plate composition is appropriately setdepending on the types and the like of the curing aid agent and thecuring agent to be used, but is, for example, preferably in the range of0.001 to 10 mass %. This makes it possible to more easily cure theback-plate composition, to thereby easily obtain the back plate 11.

Moreover, examples of the filler include, but are not particularlylimited to, an inorganic filler, an organic filler, and the like.Examples of the inorganic filler include calcium carbonate, clay,silica, mica, talc, wollastonite, glass beads, milled carbon, graphite,and the like. One type of them can be used alone, or two or more typesof them can be used in combination. Moreover, examples of the organicfillers include polyvinyl butyral, acrylonitrile butadiene rubber, pulp,wood powder, and the like. One type of them can be used alone, or two ormore types of them can be used in combination. Among them, particularly,the acrylonitrile butadiene rubber is preferably used as the filler (theorganic filler) from a viewpoint of further increasing an effect ofimproving toughness of the back plate 11 (the molded product).

In the case where the filler is used, an amount of the filler containedin the back-plate composition is not particularly limited, but ispreferably in the range of 1 to 30 mass %. This makes it possible tofurther improve the mechanical strength of the back plate 11.

Moreover, as the mold release agent, zinc stearate, calcium stearate,and the like can be used, but it is not particularly limited thereto.

In the case where the mold release agent is used, an amount of the moldrelease agent contained in the back-plate composition is notparticularly limited, but is preferably in the range of 0.01 to 5.0 mass%. This makes it possible to easily mold the back plate 11 into anyshapes.

An average thickness of the back plate 11 is not particularly limited,but is preferably in the range of 2 to 12 mm, more preferably in therange of 3 to 10 mm, and even more preferably in the range of 4 to 8 mm.If the thickness of the back plate 11 is less than the above lower limitvalue, there is a case that the heat resistance of the back plate 11 tothe frictional heat generated during braking slightly decreasesdepending on the type of the resin. On the other hand, if the thicknessof the back plate 11 exceeds the above upper limit value, the entirecaliper device 100 including the brake pad 10 becomes a slightly largesize.

As a method of preparing the back-plate composition, a powderimpregnation method utilizing rovings according to the description of,for example, JP-T 2002-509199 can be used.

The powder impregnation method utilizing the rovings is a method ofcoating a first strand and a second strand by a dry method usingfluidized-bed technology. Specifically, first, the other material(s)constituting the back-plate composition besides the first fibers and thesecond fibers is(are) directly adhered to the first strand and thesecond strand from a fluidized-bed without being kneaded in advance.Next, the other material(s) is(are) firmly adhered to the first strandand the second strand by being heated for a short period of time. Then,the first strand and the second strand, which are coated with the abovematerial(s) in this way, are passed through a condition regulatingsection including a cooling apparatus, and in some cases, including aheating apparatus. Thereafter, the cooled and coated first strand andsecond strand are collected, and then, respectively, cut to desiredlengths, to obtain coated first fibers and coated second fibers. Next,the coated first fibers and the coated second fibers are mixed with eachother. In this way, the back-plate composition can be prepared.

Moreover, examples of a method of molding the back plate 11 includecompression molding, transfer molding, and injection molding.

By performing the compression molding, it is possible to weaken a degreeof orientation of the first fibers and/or the second fibers at a time ofmolding. For this reason, anisotropy in the back plate 11 can be reducedin physical properties such as the strength distribution, moldingshrinkage and linear expansion. Moreover, the compression molding can beappropriately used when molding a back plate 11 having a thickthickness. Further, according to the compression molding, the lengths ofthe first fibers and the second fibers contained in the back-platecomposition can be more stably maintained in the back plate 11 as well.Furthermore, loss of the back-plate composition when molding it can alsobe reduced.

On the other hand, by performing the transfer molding, it is possible tocontrol dimensions of the back plate 11 to be molded with higherprecision. Thus, the transfer molding can be appropriately used formanufacturing a back plate 11 having a complex shape and a back plate 11requiring high dimensional precision. Moreover, the transfer molding canalso be appropriately used for insert molding.

Moreover, by performing the injection molding, it is possible to furthershorten molding cycles of the back plate 11. This makes it possible toimprove mass producibility of the back plate 11. The injection moldingcan also be appropriately used for molding a back plate 11 having acomplex shape. Furthermore, in the case where the back-plate compositionis injected at a high speed, it is possible to control the orientationstates of the first fibers and the second fibers in the back plate 11with higher precision, for example, it is possible to improve the degreeof orientation of the first fibers and the second fibers in the backplate 11.

Moreover, examples of a method of manufacturing the brake pad 10include, but are not particularly limited to, a method of molding theback plate 11, and then attaching (bonding) the back plate 11 to thefriction material 12, a method of integrally molding the back plate 11and the friction material 12, and the like.

Second Embodiment

Next, description will be made on a second embodiment of the brake padof the present invention.

FIG. 6 is a cross-sectional view showing the second embodiment of thebrake pad of the present invention.

Hereinafter, the second embodiment will be described with emphasisplaced on points differing from the first embodiment. No descriptionwill be made on the same points. In this regard, the same referencenumbers are applied to the same portions shown in FIG. 6 as those of thefirst embodiment.

As shown in FIG. 6, in the brake pad 10 according to this embodiment,the back plate 11 has both end regions of which thicknesses increasetoward the central region thereof in the rotational direction of thedisc 200 from each of the ends thereof in the rotational direction ofthe disc 200 by a predetermined distance. Further, the thickness of theback plate 11 does not substantially increase and decrease toward acenter thereof from each of the end regions thereof. The brake pad 10according to this embodiment is different from the above mentioned firstembodiment at this point. In such a configuration, a gradient (an angleformed by the rotational direction of the disc 200 and the bondingsurface of the back plate 11) of the bonding surface of the back plate11 at portions (the both end portions) of the back plate 11, where thethicknesses thereof increase, becomes large. As a result, it is possibleto further improve the durability of the back plate 11 against the forceapplied thereto in the rotational direction of the disc 200.

In this regard, in the above mentioned embodiments, the thicknesses ofthe both ends (the both end regions) of the back plate 11 in therotational direction of the disc 200 are substantially equal to eachother, but may be different from each other.

Further, the back plate 11 may be configured so that the thicknesses ofthe both ends thereof in the rotational direction of the disc 200 aresubstantially constant or reduced toward the central region of the backplate 11.

Hereinabove the preferred embodiments of the present invention have beendescribed, but the present invention is not limited thereto.

Moreover, in the above mentioned embodiments, the brake pad was composedof a mono-layer back plate and a mono-layer friction material, but thestructure of the brake pad is not limited thereto. For example, the backplate may be composed of a multi-layer laminated body, the frictionmaterial may be composed of a multi-layer laminated body, or both theback plate and the friction material may be composed of the multi-layerlaminated bodies.

INDUSTRIAL APPLICABILITY

According to the present invention, a brake pad includes a frictionmaterial provided on the side of the disc, and a back plate bonded tothe friction material on the opposite side of the disc. The back plateis configured so that a thickness of a central region of the back platein a rotational direction of the disc is larger than thicknesses of bothend regions of the back plate in the rotational direction of the disc.This makes it possible to provide a brake pad having high bondingstrength between the friction material and the back plate and havingexcellent durability, and a caliper device provided with the brake pad.Therefore, the present invention has industrially applicability.

1. A brake pad for braking a rotation of a disc, the brake padcomprising: a friction material provided on the side of the disc; and aback plate bonded to the friction material on the opposite side of thedisc, wherein a thickness of a central region of the back plate in arotational direction of the disc is larger than thicknesses of both endregions of the back plate in the rotational direction of the disc. 2.The brake pad as claimed in claim 1, wherein in the case where a minimumvalue of the thicknesses of the end regions of the back plate is definedas “h₁ [mm]” and a maximum value of the thickness of the central regionof the back plate is defined as “h₂ [mm]”, h₁ and h₂ satisfy arelationship of “h₂−h₁<3”.
 3. The brake pad as claimed in claim 1,wherein a minimum value of the thicknesses of the end regions of theback plate is in the range of 3 to 5 mm.
 4. The brake pad as claimed inclaim 1, wherein a maximum value of the thickness of the central regionof the back plate is in the range of 4 to 7 mm.
 5. The brake pad asclaimed in claim 1, wherein the thickness of the back plate continuouslyincreases toward the central region from each of the end regions.
 6. Thebrake pad as claimed in claim 1, wherein the back plate is formed of aback-plate composition including a resin and a plurality of fibers. 7.The brake pad as claimed in claim 6, wherein the fibers are glassfibers.
 8. The brake pad as claimed in claim 6, wherein the resincontains at least one type selected from the group consisting of phenolresin, epoxy resin, bismaleimide resin, benzoxazine resin, andunsaturated polyester resin.
 9. A caliper device comprising: the brakepad defined by claim 1; a piston that presses the brake pad toward adisc; and a caliper in which the piston is put so as to be movable.